The present disclosure relates generally to the field of radar systems. More specifically, the present disclosure relates to antenna position adjustment and/or calibration.
U.S. Pat. No. 6,424,288 invented by Daniel L. Woodell and assigned to the assignee of the present invention discloses a system for and methods of displaying radar information using weather radar systems. Weather radar systems generally include an antenna coupled to a receiver/transmitter circuit and a tilt control system. The tilt control system can be an entirely electronic system for directing radar signals from the antenna by electronically configuring the antenna or can be an electro-mechanical system that physically moves the antenna.
The tilt control system and the receiver/transmitter circuit are coupled to a processor. The processor provides transmit signals through the receiver/transmitter circuit to the antenna to transmit radar beams. The processor receives return signals derived from radar returns received by the antenna. The return signals are provided to the processor via the receiver/transmitter circuit.
The processor also provides signals to the tilt control system to control the position of the antenna. The position of the antenna can be adjusted with respect to its tilt angle. In addition, the tilt control circuit can allow adjustments to the elevation and roll of the antenna.
Current generation weather radar systems use automatic antenna tilt control to command antenna azimuth scans at desired elevation angles relative to the horizon of the weather radar system. As scans occur, aircraft orientation can change. The weather radar system can accommodate random components associated with aircraft orientation by receiving an indication of the aircraft orientation from sensors or other aircraft equipment. The radar system uses the aircraft orientation to correct antenna position so that the azimuth scan occurs across the horizon at a fixed elevation regardless of aircraft orientation.
To provide the most effective radar operation, the radar antenna should be positioned at known placements with respect to the aircraft. For example, to provide the most effective weather sensing operation, the weather radar antenna should be positioned at known placements with respect to the aircraft. All classes of automatic airborne weather radar systems have performance that is dependent upon the quality of the antenna beam position versus the environmental estimates of that position. These classes of automatic airborne weather radar systems include weather radar systems manufactured by Rockwell Collins, Inc., Honeywell International, Inc. and others.
Many factors can contribute to antenna placement or pointing errors (e.g., pointing errors with respect to the expected bore sight angle). Errors can be relatively dynamic and/or relatively constant. Some errors can be due to installation issues and mounting hardware tolerances. These errors tend to be relatively constant. Once detected, calibration with respect to errors due to installation issues and mounting hardware tolerances can be achieved.
Other pointing errors can be more dynamic. For example, airframes associated with aircraft can change shape due to pressurization, uneven heating, and loading. Applicants have found that these changes in shape of the airframe can affect the expected position of the antenna (especially the expected elevation, pitch, and roll position of the antenna). Other errors can be due to atmospheric phenomenon, such as the lensing effect associated with the atmosphere. Dynamic pointing errors and/or fixed errors can also occur due to errors associated with the sensing of the aircraft's orientation.
Heretofore, adjustment to antenna position has been performed in response to observed performance of the weather radar system. According to one conventional technique, the antenna or bore site is aimed from a known position to a known fixed target position. The actual return is analyzed to make adjustments to the antenna position. The antenna is manually or electronically trimmed to a more accurate position. According to another conventional technique, the antenna is positioned using optical tools.
Some aircraft have attitude sources (e.g., such as an attitude and heading reference system (“AHRS”)). However, some of these sources are not accurate enough in a stand alone mode, to support weather radar operations (e.g., a MultiScan weather radar manufactured by Rockwell Collins, Inc.).
Thus, there is a need for a system for and a method of adjusting the position of an antenna for optimum weather radar performance. Further still, there is a need for real time or pseudo-real time adjustments to antenna position to compensate for dynamic errors associated with weather radar systems. Yet further, there is a need for a weather radar system optimized to determine antenna offset errors. Yet further still, there is a need for a system that automatically detects antenna offset errors and provides adjustment to the antenna. There is also a need for a weather radar system that can determine errors associated with the roll, elevation, and pitch of an antenna. There is also a need for a system and/or method to measure the angle from the aircraft to ground with high accuracy for weather radar operations.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.